Power output evaluation of a porous annular thermoelectric generator for waste heat harvesting

Abstract

Comparing with traditional thermoelectric generators (TEGs) heating a solid body and extracting heat indirectly, porous TEGs can directly extract heat from gaseous/liquid medias and convert them into electric power. This paper considers the electrical and thermal contact resistances between the heat source/heat sink and TEG, and evaluates the power output of a porous annular TEG for waste heat harvesting. A theoretical model for the effects of gas velocity, the external resistance, porosity and the electrical/thermal contact resistances on power output is proposed. Analytical and simplified expressions of power output are derived. The analysis demonstrates that the porous structure can significantly enhance the performance of TEG comparing to the bulk TEG. It is found that power output is proportional to the temperature difference across the TEG and inversely proportional to the cross-sectional area of the TEG. Effect of gas velocity on the power output is relatively insignificant. The power output increases to a peak value and then decreases with porosity, external electrical resistance and cross section area of TEG. The optimized area of cross section and porosity of TEG for maximum power output are given. With the increase of external electrical resistance, porosity should be enhanced to obtain the maximum power output. Relation between the optimized porosity and pore diameter of sample is presented.